Comments by Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 28 July 2015

    Steve,

    Wow, that looks like a fun RC vehicle! The battery is probably there more to stabilize the voltage, not the current in your system. How that system works depends on the interactions of your alternator, battery, and motor controller, so I can't give you an answer based on battery capacity alone, especially because you probably have concerns beyond it working once (e.g. how long will the battery last if you use it this way?). This battery manual from Yuasa has some nice general info:

    http://www.yuasabatteries.com/pdfs/TechManual_2014.pdf

    There's a graph on page 8 that suggests you should generally be able to get 100 A even out of a crappy 10 Ah battery. That's just for 30 seconds, with the voltage allowed to drop as low as 7.2V, but if the battery alone can do that, I think it should be able to serve your purposes. Again, I don't know what that will do for the long-term life of the battery, but we just got some 12 V, 12 Ah batteries for $25 each, so you'd only be risking about $50 while taking off 75% of your battery weight. You can test how well they're serving their purpose by monitoring the stablility of your battery voltage under different loads.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 16 June 2015

    Kris,

    600 mAh is not much for a AA battery (you sure you don't mean AAA?). A higher-capacity battery with the same voltage won't blow out your LED, but you might not necessarily get anything more out of it since your solar light might be limited elsewhere. For instance, the solar panel and charge circuitry in there might need 18 hours of strong sunlight just to fully charge the 600 mAh battery, in which case you probably never even fully charge it. If you're only putting 400 mAh or so into your 600 mAh battery, you'll still only end up with the same 400 mAh in there even if you go to a 900 mAh battery.

    Separately, it's not generally the case that a system designed for one battery will automatically work with a bigger one. But the solar light is probably just trickle-charging the battery, and if you have one of the same chemistry and approximately the same capacity, it will probably be fine. However, going to something like 60 mAh or 6000 mAh (10x smaller or bigger) is more likely to result in problems that could damage the battery or your other circuitry.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 16 June 2015

    Mark,

    Did you even read the original post? It's about how A and Ah are related. Anyway, if your 2 Ah battery lasts about 6 minutes (1/10 of an hour), your motor draws about 20A. If the battery lasts 12 minutes, the motor draws about 10A. These would just be the average current over that discharge time, and the motor might draw much more when under heavy load or when it's starting up. You could try the 10A supply you have and see if it's enough, but it's quite possible you would need a much beefier power supply to match what the battery can deliver.

    - Jan

  • New product: Logic Level Shifter, 4-Channel, Bidirectional

    New product: Logic Level Shifter, 4-Channel, Bidirectional

    - 1 June 2015

    Nick,

    Is there a specific parameter you are concerned about? We do not want to commit to particular components for boards like these, but the specs should be in line with typical components like this (dual low-voltage MOSFET in a small package).

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 25 April 2015

    Charging time is going to depend on the capacity of your battery in basically the same way as discharge time. A 10 Ah battery you charge at two amps is going to take something over five hours to charge; a 5 Ah battery charged at the same rate will take maybe three hours. There will be some maximum rate at which you can charge the battery, and that will be proportional to C, just like the maximum discharging current I mentioned in the post. Lead-acid batteries are pretty tolerant of all kinds of charging, so you can charge them in an hour, though you should make sure not to keep charging them at that rate. For example, that 8 Ah battery I have pictured should probably be fine getting charged at 8 A, though you can see the manufacturer has 2.4A printed on the battery.

    Since you already have a charger that is probably limited to about 1 A of charge current, you should just look for the smallest battery that can last long enough for your purposes. Once the capacity gets below about 3 Ah, you'll have to be more careful not to overcharge it (i.e. don't keep trying to charge it after it's already charged).

    - Jan

  • Thoughts on Open-Source Hardware

    Thoughts on Open-Source Hardware

    - 16 February 2015

    Alex,

    Thanks for your thoughtful post.

    I am not suggesting that some "magic software" do the net connecting. I think getting the schematic to the right place, making the logical net connections and other corresponding design decisions, might be roughly analogous to the code merging you talk about. But there's still a lot of work to do in the layout and routing, which I think would be more analogous to compiling, and I think there is a very fundamental difference in the amount of magic software available to do compiling vs. auto placing and routing.

    I don't personally do it, but more software-oriented people here tell me that merging more than 100 lines of code changes is normal and not at all a nightmare. On the other hand, adding a resistor to some of our hardware designs can be much harder, necessitating moving lots of other components and redoing a lot of routing and reevaluating integrity of things like polygon areas and current paths. It's more like making changes in a program written in assembly for a microcontroller that is already full.

    Of course we can find cases in any domain where merging projects is difficult; the point is, when is it relatively easy and practical? On larger software projects, different people are merging hundreds of lines of changes many times a day and it's completely routine. I don't see anything equivalent to that happening in hardware projects; do you?

    Are there even any examples of hardware projects that merge in changes from external contributors? Looking at something like Arduino, we can easily see tons of software merging history and none for the hardware side.

    - Jan

  • New product: Hydra Smart DC Power Supply

    New product: Hydra Smart DC Power Supply

    - 14 January 2015

    Clyde,

    Here's another ripoff: those $20 of parts are themselves made up of only $2 worth of raw materials!

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 27 December 2014

    Hi, Nate.

    If you get two of the same battery, you will have double the energy of one battery, no matter how you arrange them. You do not get to double the voltage AND double the amp-hours, which would be quadrupling the energy stored. If you put the two batteries in series, you will get double the voltage and the same Ah; if you put the batteries in parallel, you will get the same voltage and double the Ah.

    By the way, you should be very careful about putting various packs in series or parallel. Particularly in the parallel configuration, you are basically shorting together two batteries that are unlikely to have the exact same voltage. Lithium batteries are especially touchy about being correctly charged and discharged, so I strongly recommend getting a single pack that fits your application rather than trying to assemble your own large pack out of smaller batteries.

    - Jan

  • RC servo speed control

    RC servo speed control

    - 2 December 2014

    Paco,

    The hobby servos I wrote about in this article are not well suited for doing what you are asking for since they do not tell you the error. You can do something similar to the speed control I wrote about by picking a virtual set point and then sending your servo appropriate commands based on where you think the servo should be, having it move faster when farther from the point and slower when near that set point. However, this is all just an open-loop motion sequence you would be sending the servo, and depending on the resistance it encounters, the actual resulting movement can be completely different from what you intend.

    If you are looking to effectively make your own servo by doing your own closed-loop control system, that is outside the scope of this article, and you should search online for things like "closed-loop motor control with Arduino" as there are many resources available.

    - Jan

  • Understanding battery capacity: Ah is not A

    Understanding battery capacity: Ah is not A

    - 18 November 2014

    Caroline,

    You're missing the voltages of the batteries. It's hard to tell much without that. For instance, if your 6 Ah battery is 36 V and your 9 Ah battery is 24 V, they will both have the same capacity. If that were the case, your 9 Ah battery would indeed last longer, but you would be going a lot slower, for no net increase in range. This is is all assuming the bike would even go at 24 V. If both batteries are 36 V, the 9 Ah unit should give you about 50% more time and range. Keep in mind that in that case, the battery should also be about 50% bigger and heavier.

    - Jan

New Products

Pololu Dual MC33926 Motor Driver for Raspberry Pi (Partial Kit)
30:1 Micro Metal Gearmotor HPCB
12mm Hex Wheel Adapter for 6mm Shaft (2-Pack)
RoboClaw 2x5A Motor Controller (V5)
Hakko 599B-02 Solder Tip Cleaning Wire Sponge with Holder
Hakko T18-D12 Soldering Tip
Screw Terminal Block: 5-Pin, 0.1″ Pitch, Side Entry (2-Pack)
Hakko T18-D32 Soldering Tip
BD65496MUV Single Brushed DC Motor Driver Carrier
298:1 Micro Metal Gearmotor HPCB
Log In
Pololu Robotics & Electronics
Shopping cart
(702) 262-6648
Same-day shipping, worldwide
Menu
Shop Blog Forum Support
My account Comments or questions? About Pololu Contact Ordering information Distributors